As electronic products are required to be downsized and have high performance, semiconductor devices mounted on a substrate are downsized and the number of terminals is increasing. Therefore, the terminals are required to be downsized and integrated.
As solder balls are downsized, it is difficult to maintain sphericity and it is required to prevent solder balls from being bridged and to reliably connect the substrate and the semiconductor devices. Therefore, it is required to improve material characteristics of the solder balls.